The elastic properties of the two-dimensional erythrocyte membrane are characterized by two intrinsic material constants: a shear modulus and an area compressibility modulus. The shear modulus characterizes the membrane's resistance to deformation at constant surface area (which results when the membrane tension is uniaxial or nearly so) while the area compressibility modulus characterizes the membrane's resistance to an increase in area under the action of large, isotropic (biaxial) membrane tensions. Our working hypothesis is that the magnitude of the shear modulus reflects the state of the solid membrane component (e.g., a protein like spectrin) while the area compressibility modulus reflects the state of both the solid (protein) and "fluid sealer" (lipid) components of the membrane. The objective of the proposed study is to determine the values of these two moduli for abnormal erythrocytes. The erythrocytes under study will include 1) red cell with distinctive morphology (e.g., hereditary elliptocytes, hereditary spherocytes, irreversibly sickled cells) 2) red cells with normal morphology, but suspected intrinsic membrane abnormality (e.g., erythrocytes from patients with Duchenne or myotonic muscular dystrophy) and 3) normal red cells perturbed with echinocytogenic or stomatocytogenic agents or heat. The micropipette suction technique will be used to determine both moduli. The change in length of aspirated membrane with change in pressure drop across the cell is measured.